In the pouring of molten steel during a continuous casting process from a ladle into a tundish and subsequently from a tundish into the mold, particularly where the molten steel is aluminum killed; it is important to prevent alumina deposits from building up in the bore of the nozzle employed since excessive buildup can clog the nozzle and shut down an entire casting operation. Additionally in some applications, submersible nozzles also referred to as pouring tubes or shrouds are employed to continuously surround the stream of molten metal leaving the ladle or tundish for preventing contamination of the stream or partial oxidation due to exposure to the atmosphere. Again, it is desirable to prevent them from clogging or from erosion by direct contract with the molten metal stream.
Efforts have been made to prevent the buildup of alumina in nozzles by providing means for the injection of an inert gas such as argon into the bore. U.S. Pat. No. 3,838,798 issued to Wendell G. Vos on Oct. 1, 1974, and assigned to the present assignee represents one such effort in which the nozzle includes a ceramic annulus surrounding the bore and into which an inert gas is supplied. U.S. Pat. No. 3,253,307 issued to D. K. Griffiths et al on May 31, 1966, suggests a multiple piece, physically joined nozzle to define a means for regulating a stream of molten metal poured therethrough by the injecting of the inert gas into the nozzle bore. Two-piece nozzles have been made and joined by cementing after each piece is separately fired. In such nozzles the pieces define a bore portion and a body portion with a space therebetween for providing a manifold surrounding the bore and into which a pressurized inert gas can be supplied for injection into the bore of the nozzle.
Although these approaches represented by the prior art have significantly reduced the deposit of alumina in nozzles and permitted more efficient continuous casting, their success has been limited due in part to the manner in which they are manufactured, either making them failure prone or very difficult to make. Nozzles with cemented junctions frequently crack in use due to the different temperature expansion characteristics of the materials and the cement. Such nozzles thus are relatively expensive to manufacture and have not met with success.